Washington — Drug cartels have turned to a new and effective vehicle to smuggle their goods, using small, homemade "semi-submersibles" that are hard to detect and yet effective at carrying millions of dollars worth of cocaine and other illicit drugs that end up in the United States.

Military officials who oversee Latin and South America have grown alarmed by the increased use of these boats, which poke out above the water only a foot or so but carry more than 12 tons of cargo. The military's ability to interdict the craft is hampered in part because its attention has been focused on the wars in Iraq and Afghanistan and on border security.

"We're in a holding pattern," says Rear Adm. Joseph Nimmich, who heads a military joint task force in the Florida Keys overseeing the drug fight. "We are maintaining our own but not making huge progress."

The semi-subs, known as "self-propelled semi-submersibles," also represent a serious national security threat: Today it's drugs, but tomorrow's cargo could be heavy weaponry, senior defense officials warn.

Military officials, working in conjunction with the US Coast Guard and law-enforcement agencies, say they apprehended about 25 of the hard-to-find semi-subs a couple of years ago but this year are on track to find as many as 60. Another military official says that number could be as high as 100 by the end of the year.

Meanwhile, the semi-subs have an estimated success rate – actual delivery of cargo – of about 80 percent, Admiral Nimmich says, adding that he is confident the US can tackle the problem given more focus and resources.

Most of the boats have been intercepted in the eastern Pacific between South and Central America. In the last two years, the vessels have emerged as an increasingly viable way to transport large quantities of drugs that ultimately make their way into the US.

Built of a combination of fiberglass and wood and now steel, the 40- to 80-foot long semi-subs can travel as far as 2,000 miles, carrying a payload that represents, according to Nimmich, "10 hits of cocaine for every senior high school student in the US."

Costing an average of $2 million per ship, the semi-subs are typically built under cover of the jungle canopy in South and Central America and can take a year to construct.

Drug cartels are using them increasingly, military officials say, because the US Southern Command and other government agencies have successfully foiled other methods, including so-called Go Fast boats, high-performance craft that have been used to smuggle drugs for years.

Lack of consensus in how to respond

But the US is challenged in responding to a constantly adapting enemy.

That's due in part to the focus on the wars overseas; in part to a lack of consensus about how to approach the problem, drug and defense experts say.

For example: even before 9/11, then Defense Secretary Donald Rumsfeld had discouraged actively battling drug cartels. Today's antidrug effort continues to be divided over questions about whether to emphasize reducing the supply or the demand for drugs.

American drug policy needs a rethinking of strategy on both the demand and supply sides, says Peter Hakim, president of Inter-American Dialogue, a Washington-based policy group. "US drug policy is something of a disaster in terms of any concrete results or progress." [Editor's note: The original version misstated Mr. Hakim’s view on US drug policy.]

The wars have weakened the effort even more.

"Given Iraq, Afghanistan, and the war on terror, they completely walked away from Latin American policy," says Barry McCaffrey, a retired Army four-star general who also served as the so-called drug czar in the White House under Presidents Clinton and George W. Bush.

Although US Southern Command, headed by Adm. James Stavridis, has not received as much attention support as its sister commands, particularly US Central Command, which oversees the wars in Iraq and Afghanistan, it has quietly focused on the drug fight, interdicting about 200 metric tons of cocaine last year.

To make more headway, General McCaffrey says, the American government as a whole needs a broader strategic policy in Latin America that would help address the growth in effectiveness of drug cartels.

If semi-subs represent one way in which narcotics traffickers have adapted, the growing use of tunnels on the US-Mexico border represent another.

"These narcotics traffickers, much like terrorists in other parts of the world, are learning adversaries," said Gen. Victor "Gene" Renuart, head of US Northern Command, on C-SPAN's "Newsmakers" program on Sunday. "As you close one loop, they will open another."

General Renuart, who among other things focuses on border-security issues, said: "If we believe we have solved the problem, we are almost guaranteeing it will come back. You can't take your eye off the ball in this kind of situation."